A Fan Algorithm for Chow-Witt Rings of Smooth Projective Toric Varieties

Abstract

Let $R$ be a real closed field and let $X_{\Sigma }$ be a smooth projective split toric variety. For an explicitly chosen basis rigidification $\mathfrak{r}$ of its Picard grading, we prove that the pair $(\Sigma ,\mathfrak{r})$ determines the resulting total Chow--Witt ring and give a terminating finite algorithm for all groups, products, twists, and forgetful maps. The ring is identified with an explicit fibre product of the Picard-graded diagonal $\mathbf{I}$-cohomology ring and the integral inverse images of twisted Bockstein kernels over the mod-$2$ Chow ring. Using real cycle classes, we identify the first factor with the cohomology of the real toric variety with all sign local systems. We construct the mod-$2$ cycle map on invariant divisors as explicit deck-transition cocycles and obtain finite signed boundary and product matrices directly from the fan.